Tooth eruption is a series of complicated physiological processes occurring once the crown is formed completely, as well as when the tooth moves toward the occasion plane. As such, the tooth moves through the alveolar bone and the oral mucosa until it finally reaches its functional position. Most studies indicate that the process of tooth eruption involves the alveolar bone, dental follicles, osteoclasts, osteoblasts, and multiple cytokines. Dental follicles regulate both resorption and formation of the alveolar bone, which is required for tooth eruption. Furthermore, root formation with periodontal ligament facilitates continuous tooth eruption. However, the exact mechanism underlying tooth eruption remains unclear. Hence, this review describes the recent research progress on the cellular and molecular mechanisms of tooth eruption.
Dental Sac ; Humans ; Osteoblasts ; Osteoclasts ; Periodontal Ligament ; Tooth ; Tooth Eruption ; physiology ; Tooth Root

OBJECTIVETo compare the ultra-microscopic changes of periodontal Ruffini's corpuscle induced by different patterns of tooth movement, and investigate the influence of different changes of the periodontal mechanical environment on the periodontal mechanoreceptor.

METHODSThirty-two eight-weeks-old SD rats were divided into control group (n = 4), none-extraction group (n = 12) and extraction group (n = 12), and none-extraction group and extraction group were further divided into three subgroups, namely 3 day and 14 day and 28 day. For control group, no intervention was performed. For none-extraction group and extraction group, the following interventions were conducted. In none-extraction group, the maxillary left and mandibular right third molars were moved distally. In extraction group, the maxillary left third molar was moved distally, and the bilateral mandibular third molars were extracted. The ultra-structures of periodontal Ruffini's corpuscle in the periodontal ligament of the distal root of the bilateral maxillary third molars were observed under the transmission electron microscope.

RESULTSThe ultra-structrural changes in the none-extraction group were mainly characterized by degeneration or abnormal distribution of mitochondria in the axon terminal, which were almost recovered at 28 d. In the extraction group, the changes were mainly characterized by deficiency or abnormal elongation of the Schwann sheath and were not recovered at 28 d.

CONCLUSIONSThe ultra-structures of periodontal Ruffini's corpuscle might be influenced by tooth movement and occlusal changes, and the mechanorecepting function of it might be affected by changes of the periodontal mechanical environment.

Animals ; Mechanoreceptors ; physiology ; Molar ; Molar, Third ; Periodontal Ligament ; Rats ; Tooth Movement Techniques ; Tooth Root

In order to study mechanical stress on root from orthodontic tooth movement by sliding mechanics, a 3-dimensional finite element model incorporating all layers of a human mandibular dental arch with orthodontic appliance has been developed to simulate mechanical stress on root from the orthodontic tooth movement. Simulated orthodontic force of 2 N at 0, 30 and 45 degree from the horizontal axis was applied to the crown of the teeth. The finite element analysis showed when orthodontic forces were applied to the tooth, the stress was mainly concentrated at the neck of the tooth decreasing uniformly to the apex and crown. The highest stress on the root was 0.621 N/mm(2) for cervical margin of the canine, and 0.114 N/mm(2) for apical region of the canine. The top of canine crown showed the largest amount of displacement (2.417 microm), while the lowest amount of displacement was located at the apical region of canine (0.043 microm). In conclusion, this model might enable one to simulate orthodontic tooth movements clinically. Sliding force at 2 N is ideal to ensure the bodily orthodontic tooth movement. The highest stress concentration in the roots was always localized at the cervical margin when orthodontic force of 2 N at 0, 30 and 45 degree from the horizontal axis, so there may be the same risk of root resorption when orthodontic force of 2 N at 0, 30 and 45 degree was used in clinic cases.
Computer Simulation ; Dental Arch/*physiology ; Finite Element Analysis ; Orthodontic Anchorage Procedures ; Orthodontic Appliances ; Stress, Mechanical ; Tooth Movement ; Tooth Root/*physiology

OBJECTIVETo observe the effect of matrix metalloproteinase-1 (MMP-1) from human host on degradation of dentin organic matrix of root dentin.

METHODSThe freshly extracted caries-free impacted teeth were selected. Teeth were cut transversely under the enamel-cementum junction into dentin sections with a thickness of about 5 mm. Then all sections with removal of cementum, pulp and predentin were randomly divided into four groups. In the first group, dentin sections were demineralized with acid solution for 21 days, and then incubated with MMP-1 solution for 7 days; the second group were only treated with acid solution for 21 days; the third group were only attacked by MMP-1 solution for 7 days; and the fourth group were untreated as a control. Then all sections were dehydrated in ascending strength of alcohol, critically dried, coated with platinum, and then observed under scanning electron microscope(SEM).

RESULTSThe dentin sections of root surface attacked by acid and MMP-1 showed that demineralization of dentin mineral and degradation of dentin matrix fibrae synchronously happened. The dentin matrix fibrae wasn't degradated in the groups treated with acid or MMP-1.

CONCLUSIONThe proteinases from human host may play an important role in the development of root surface caries. MMP-1 may distinctly degradate the organic matrix of demineralized dentin.

Dental Cementum ; Dental Enamel ; Dentin ; enzymology ; Humans ; Matrix Metalloproteinase 1 ; physiology ; Microscopy, Electrochemical, Scanning ; Root Caries ; enzymology ; Tooth Root ; enzymology

This experiment was aimed to shed light on the correlation and quantitative relationships between the width of bovine periodontal ligament (PDL) and the elastic modulus and, more over, between the width of bovine PDL and the capacity ratio of collagen fibers. The width and length of periodontal ligament of PDL were determined by stereomicroscope, and the elastic modulus by the materials testing systems. The collagen fibers in cross section of the specimen were stained with 1% Sirius Red F3B in saturated carbazotic acid, and the photo of stained PDL was collected by stereomicroscope. Image pro plus6.0 image analysis software was used to measure and calculate the capacity ratio of collagen fibers. It was found that there is a negative correlation between the width of bovine periodontal ligament and elastic modulus. The correlation coefficient is -0.21 and the simple linear regression model is Y = 71. 681-0.021x (Width of PDL); there is a positive correlation between capacity ratio of collagen fibers and elastic modulus. The coefficient correlation is 1.583 and the simple linear regression model is Y = -34.944 + 1.583x (The percentage of collagen fibers). Thus, the elastic modulus of bovine PDL increases while the width of bovine PDL decreases, and it increases while the capacity ratio of collagen fibers increases.
Animals ; Cattle ; Collagen ; chemistry ; Elastic Modulus ; Periodontal Ligament ; physiology ; Tensile Strength ; Tooth Root ; anatomy & histology

The bone morphogenetic protein (BMP) family is an important factor in the regulation of cell ular life activities and in the development of almost all tissues. BMP-mediated signaling plays an important role in tooth root development, which is a part of tooth development. Epithelial and mesenchymal interactions are involved in tooth root development, but the BMP signaling pathway has a different effect on tooth root development in epithelial and mesenchymal. This review summarizes the advances of BMP signaling in tooth root development.
Bone Morphogenetic Protein 2 ; Bone Morphogenetic Protein 7 ; Bone Morphogenetic Proteins ; physiology ; Odontogenesis ; Signal Transduction ; Tooth ; Tooth Root ; growth & development

OBJECTIVETo evaluate the bone density changes in the apical area of subgingivally fractured tooth after rapid orthodontic extrusion.

METHODSTwelve fractured incisors in 11 patients extended 2 - 5 mm below the gingival line were selected. Two weeks after root canal therapy, the subgingival fragment was lifted up and the fracture line was brought 1.5 - 2.0 mm above the level of the gingival line by means of edgewise fixed appliance. After the extrusion completed, the tooth had been stabilized and held for 6 months. The CT Analyser software was used to measure the bone density changes in the apical area on radiographs once a month. Changes of relative value in bone density was quantitatively analyzed.

RESULTSThe average period of extrusion was 11 days. The relative value of bone density in the apical region was -39.6% immediately after extrusion and continuously increased afterwards. In the third month, the value (18.5%) changed most rapidly (P < 0.01).

CONCLUSIONSUnder the continuous and proper tooth axial extrusion force, the tooth moved rapidly and steadily. The bone density in the apical area approached normal value within 3 months after treatment.

Adult ; Bone Density ; physiology ; Female ; Humans ; Incisor ; immunology ; Male ; Orthodontic Extrusion ; methods ; Orthodontic Wires ; Tooth Fractures ; physiopathology ; therapy ; Tooth Root ; injuries ; Tooth Socket ; physiopathology

The root is crucial for the physiological function of the tooth, and a healthy root allows an artificial crown to function as required clinically. Tooth crown development has been studied intensively during the last few decades, but root development remains not well understood. Here we review the root development processes, including cell fate determination, induction of odontoblast and cementoblast differentiation, interaction of root epithelium and mesenchyme, and other molecular mechanisms. This review summarizes our current understanding of the signaling cascades and mechanisms involved in root development. It also sets the stage for de novo tooth regeneration.
Cell Differentiation ; genetics ; Dental Cementum ; physiology ; Epithelium ; physiology ; Humans ; Mesoderm ; physiology ; Molecular Biology ; Odontoblasts ; physiology ; Odontogenesis ; genetics ; Signal Transduction ; genetics ; Tooth Root ; embryology ; growth & development

BACKGROUNDAnimal models are needed for the study of rapid tooth movement into the extraction socket through distraction osteogenesis of the periodontal ligament.

METHODSModified distraction devices were placed on eight dogs between the first and third mandibular premolars on the left sides; similar placement of traditional straight wise appliances on the right sides served as the control. The experimental distractors were activated (0.25 mm/d) twice a day and the control devices were activated (100 g) for two weeks with consolidation periods at weeks two, three, six, and ten. Two dogs were sacrificed at each consolidation time point; rates and patterns of tooth movement, loss of anchorage, and periapical films were evaluated, and the affected premolars and surrounding periodontal tissues were decalcified and examined histologically. General observations, X-ray periapical filming and histology examination were performed.

RESULTSDistal movement ((3.66+/-0.14) mm) measured two weeks after modified distraction exceeded that achieved using the traditional device ((1.15+/-0.21) mm; P<0.05). Loss of anchorage was minimally averaged (0.34+/-0.06) mm and (0.32+/-0.07) mm in the experimental and control sides, respectively. By radiography, apical and lateral surface root resorptions on both sides were minimal. Alveolar bone lesions were never evident. Fibroblasts were enriched in periodontal ligaments and bone spicules formed actively along directions of distraction.

CONCLUSIONSThe canine model is suitable for the study of rapid tooth movement through distraction osteogenesis of the periodontal ligament. The technique accelerates tooth movement, periodontal remodeling, alveolar bone absorption, and may induce fibroblast formation, as compared to the traditional orthodontic method, without adversely affecting root absorption, bone loss, tooth mobility and anchorage loss.

Animals ; Dogs ; Male ; Osteogenesis, Distraction ; methods ; Periodontal Ligament ; physiology ; surgery ; Root Resorption ; etiology ; Tooth Movement Techniques ; methods

BACKGROUNDIt is very difficult and relatively unpredictable to preserve and restore severely weakened pulpless roots. To provide much needed benefit basis for clinical practice, this study was carried out to analyze the stress distribution in weakened roots restored with different cements in combination with titanium alloy posts. Finite element analysis (FEA) was employed in the study.

METHODSA pseudo three-dimensional model of a maxillary central incisor with flared root canal, theoretically restored with titanium alloy posts in combination with different cements, was established. The analysis was performed by use of ANSYS software. The tooth was assumed to be isotropic, homogenous and elastic. A load of 100 N at an angle of 45 degrees to the longitudinal axis was applied at the palatal surface of the crown. The distributions of stresses in weakened roots filled with cements of different elastic modulus were analyzed by the three-dimensional FEA model.

RESULTSSeveral stress trends were observed when the stress cloud atlas obtained in the study was analyzed. With the increase of the elastic modulus of cements from 1.8 GPa to 22.4 GPa, the stress values in dentin decreased from 39.58 MPa to 31.43 MPa and from 24.51 MPa to 20.76 MPa (respectively, for maximum principle stress values and Von Mises stress values). When Panavia F and zinc phosphate cement were used, the stress peak values in dentin were very small with no significant difference observed, and the Von Mises stress values were 20.87 MPa and 20.76 MPa respectively. On the other hand, maximum principle stress value and Von Mises stress value in cement layer increased with the increase of the elastic modulus of cements.

CONCLUSIONSThe result of this study demonstrated that elastic modulus was indeed one of the important parameters to evaluate property of the cements. Our three-dimensional FEA model study also found that the cement with elastic modulus similar to that of dentin could reinforce weakened root and reduce the stress in dentin. Thus, it may be a better choice for the restoration of weakened roots in clinical practice.

Adult ; Dental Cements ; Dental Stress Analysis ; Elasticity ; Finite Element Analysis ; Humans ; Post and Core Technique ; Titanium ; Tooth Root ; physiology